Much of the skill in archery has necessarily been centered in developing an accurate judgement of distance, combined with a sense of the proper placement of the bow to send the arrow on a trajectory corresponding to that distance. Traditionally, the archer has developed a sort of sixth sense based upon sighting across the tip of the arrow, with the bow held to direct the arrow along a path that the archer intuitively senses to correspond with his judgement of distance. It is common knowledge that a wide range of error is to be expected in making these related judgements. A judgement of distance alone, for example, must often be made instantly, and subject to a number of optical illusions resulting from the presence of surrounding bushes and trees, and the contour of the ground. Movement of the animal being hunted is another complicating factor.
Various forms of sighting devices for bows have been considered for some time, but none of these have done much to reduce the high degree of skill necessary to correlate arrow trajectory and distance judgement, to say nothing of establishing the observed distance to begin with. Most of these devices are primarily a series of vertically-spaced reference lines positioned in such a way that the archer's eye, in sighting across the tip of the arrow, can associate the line of sight with a particular one of these cross-reference lines associated by appropriate marking with stated distances. The archer must first form an accurate judgement as to the distance, and then find the appropriate cross-reference line with his line of sight in order to establish the correct attitude of the bow to launch the arrow on the desired trajectory path.